1. Field of the Invention
The present invention relates to a connection method between a rotor holder and a cup portion of an impeller of a fan.
2. Description of the Related Art
Conventionally, electronic devices have been generating higher amounts of heat as the number and/or capacity of their electronic components and processing units has expanded to meet current demand for higher performance devices. To this end, a fan is typically used to cool the electronic components and processor units of an electronic device. In order to achieve the characteristics (air quantity, static pressure, etc) required of the fan incorporated in the electronic devices, the fan is expected to rotate at a high speed. On the other hand, the fans incorporated in the electronic devices that are used at home and/or office environments are expected to operate quietly. To meet such expectations (i.e., reduction of high frequency noise, etc) while achieving the aforementioned characteristics, a large fan, for example, rotating at a low speed may be effective.
One of the factors for the noise which is heard when the fan rotates at a high speed is generated by the blades of the fan coming into contact with air at the high speed. Also, when the fan rotates at a low speed, other factors generate noise, such as electromagnetic sound generated by a control circuit, sliding sound generated by a bearing portion of the motor, vibration sound generated by other components of the motor. In particular, the vibration sound generated by either a rotor holder or an impeller of the motor which are assembled with one another is noticeable.
In general, it is a difficult task to join an impeller made of a resin material with a rotor holder of a large size fan (e.g., a fan whose impeller has a diameter greater than 110 mm).
Also, in general, a fan includes a cup portion having a substantially cylindrical shape, a plurality of blades arranged outside of the cup portion, and a rotor holder having a substantially cylindrical shape press fitted into the inner circumferential surface of the cup portion. When a size of the fan increases and when a force required to press fit the rotor holder into the impeller, the cup portion may be damaged (i.e., deformed, cracked or the like). On the other hand, when a force used to press fit the rotor holder into the impeller is compromised, the impeller may be removed easily from the rotor holder. That is to say, a force used to press fit the rotor holder with respect to the impeller cup portion is determined by the material used to form the impeller and the rotor holder and the size thereof, and includes a narrow range of acceptable amount.
For example, although an about equal amount of force may deform (i.e., crack or the like) the cup portion almost regardless of the size of the fan, a force required to retain the rotor holder with respect to the cup portion differs depending on a diameter of the inner circumferential surface of the cup portion. For such reason, the amount of force used to press fit the rotor holder into the cup portion is increased in accordance with the diameter of the inner circumferential surface of the cup portion in order to increase the amount of stress applied to the cup portion. Alternately, a thickness (i.e., a distance between the external surface and the inner surface of the cup portion) of the cup portion may be increased. Therefore, the conventional method joining the rotor holder and the cup portion is problematic.
Further, since it is highly difficult to join an impeller and a rotor holder by press fitting the rotor holder into the cup portion of the impeller, large size fans include a shaft which is affixed to an impeller via a boss portion by an insert molding. In particular, the rotor holder includes a through hole at which the boss portion is arranged. Then, a portion of the boss portion is plastically deformed at which the rotor holder is secured. In other words, the rotor holder is caulked with the boss portion.
Such method, however, allows the vibrations generated by the cup portion of the impeller and that generated by other components of the motor to resonate, which, when the impeller rotates at a low speed, becomes particularly noticeable.